Investments in equity securities - Fair value by segment (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Summary of Investment Holdings [Line Items]
Investments in equity securities	$ 117,505		$ 88,346
Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Investments in equity securities	115,464		87,081
Railroad, Utilities and Energy [Member] | Other Assets [Member]
Summary of Investment Holdings [Line Items]
Investments in equity securities	1,103	[1]	675	[1]
Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Investments in equity securities	$ 938		$ 590

[1] Included in other assets.